It may be that your webserver's IP (or the proxy IP, if proxy is used) is on a block list to umbra.nascom.nasa.gov. If so, your hoster and NASA would have to resolve that issue.
Meanwhile, if there's a cached image for the sun, then changing sunposa.php from
filemtime($cacheFileDir."jpsun.png") <= time() - 3600 or
to
filemtime($cacheFileDir."jpsun.png") <= time() - 999999 or
will stop fetching the cache for a long time.